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- Опубликовано: 17 окт 2024
- This is a tutorial and demonstration of the basics of the Resolution BW (RBW) and Video BW (VBW) functions in a Spectrum Analyzer. You may wish to review the "Basics of a Spectrum Analyzer" video if you are unfamiliar with the basic functions and block diagram of a swept spectrum analyzer. Here is the link for that video:
• #22: Spectrum Analyzer...
This video covers the definition of these terms, where they exist in the analyzer, what they do, and the effects they have on the displayed results. 
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For years I have still been referring trainee's to this video.....that cutout demo is still the best teaching aid I have ever seen........
it really is. brilliant and very simple.
I’ve used spectrum analyzers for years and have always had to spend 30 mins remembering what VBW and RBW were now that’s I’ve seen this video I know I will only spend a max of 8mins and 37 seconds
This is the most concise, helpful explanation I have ever found for RBW and VBW filters. I've been using spectrum analyzers for years and I'm quite familiar with their setup and use, but I've never understood what those filters actually did under the hood so to speak... until today. Thank you, and please keep making videos. Those of us who take the time to search out this information (the small crowd that we are) really do appreciate the time and energy you put into making them. Thumbs up!
Thank you. Be sure to let me know if you have a topic you'd like to see in a future video.
I'm sure I'll have lots of questions when I start college. I intend to get into RF engineering, provided I can make the grades. For now I'm just a curious satcom tech with all together too much time on my hands, and I'm thoroughly enjoying the wealth of knowledge available on RUclips, the EEVblog (thanks Dave) and other forums. I really enjoy the in depth technical focus of your videos. I do have one question about this video. Why do we have to convert Vpp to Vrms in order to do a dBv measurement? Is there a technical reason for it, or is it just convention?
It's because the dB values always relate to power, and power is computed from rms values.
That makes perfect sense combined with the tidbits I just learned from some other videos on the difference between Vpp and Vrms (specifically how Vrms is calculated, and why). Thanks!
when somebody knows his stuff very well, he is able to explain it in a simple, easy to understand and yet complete way.
Here we have the perfect example.
I've been teaching people how to use a spectrum analyzer and what RBW and VBW filters do for a couple of decades. This is easily the best , simplest description of it I've ever seen. Thanks!
I finally scratched a very long-standing itch by buying my own spectrum analyser a few weeks back. It's fascinating to run it in the shack on wide bandwidth (up to 1.5GHz) with a small telescopic antenna and see all the spectrum mush in a modern home! Your videos are an excellent way for me to rediscover the nuances of my new toy some 40 years after I last used a spectrum analyser professionally. Thank you and 73 de G3WGV.
A very articulate and detailed explanation to help understand spectrum analyzer operation. Thank you, Alan.
Thank you for very clearly explaining what the RBW and VBW filters are. Really appreciate the time and energy you put into making such wonderfully informative videos.
Today’s a better day sir because you helped clearly explain the workings of RBW and VBW filtering to me. I am most appreciative 🤗.
These are the best electronics videos on YT. Concise and well presented.
Well Done Alan...The new generation of entry level Spec Analyzers are priced down to a level where a whole new group of people can obtain them. This creates a need for tutorials for both the Theory of Operation and How to Use the device and get the most out of it. This video is an excellent example of how to clearly and concisely address the matter. Thanks again
You are one of the best teachers on youtube. Clear, concise, zero BS, visual, interesting. Thanks for sharing your knowledge!!
Great video. Explain the concepts of VBW and RBW in an easy way. Definitely recommend this video for anyone want to understand the spectrum analyzer more.
This is one of the best explanations of any RF fundamentals I have come across. Thank you!
Thanks - I hope you like more of my RF (and other) videos.
Brilliant explanation Alan...just starting to play with my MDO analyser..searched for "frequency analyzer rbw" and look who I find?! ;-)
Cheers, Martin.
Martin, while the principles are largely the same, the SA in the MDO operates differently. There is no "sweep". It uses a discrete Fourier Transform (actually a Chirp-Z transform to be exact) to compute the spectrum from direct sampled data. Thus, there is no VBW function, and 'sweep time' is replaced with 'spectrum update rate.' The RBW determines the time-duration of the data record that is sent to the Chirp-Z transform.
*****
Thanks for the info Alan.
Alan, you really know how to come up with simple and elegant visual aids. Masterful, concise video showing the relatively simple concept behind the oblique phrase "Resolution Bandwidth" and the application of filters. I love filters. You can't do enough videos about filters, "Q", all that cool stuff.
Very good video. After 3 years in the instrumentation industry, I have finally found something to solidify these principles in my head.
As a SATCOM guy, I thank you for the service these videos you make provide.
Your welcome - thank you for saying so.
Just purchased my first spectrum analyzer and was confused by the difference between RBW and VBW. Your video explained it very well. Thank you!
Amazing videos! As a studying engineer seeing how things work in the real world is worth more than you can imagine. Thanks for your hard work and comprehensive tutorials!
Man...best explanation of these two subjects I've come across yet.
I think this just helped me understand why my duplexer tuning was never as good as it could've been. Lowering the RBW would help me see the filters individually when they are right next to each other. Thank you!!!
Excellent video. I am currently debugging my DUT for CE compliance and this is the best explanation I have seen for VBW and RBW. Good job.
K1MGY - good questions. I'll answer them using your numbers:
1) It is an Advantest U3461
2) VBW reduces the variation in the trace due to noise, it doesn't reduce the noise floor. It won't reduce the amplitude of the signals as long as the sweep speed is slow enough to allow the filter to fully charge. This is usually taken care of automatically.
3) Reducing VBW will help uncover things that are standing "in the grass" by flattening the noisy grass around the signal. Reducing RBW will help even more by reducing the noise floor, uncovering signals that were buried below the noise.
4) Sweep time (sweep speed) is typically linked to RBW and VBW. RBW is typically linked to SPAN. Narrow SPAN = narrow RBW = slower sweep speeds. Yes, slower sweep speeds in a swept analyzer make it easier to find transients.
Alan
***** Hey Allan,
Thanks a lot for the great videos, as always. What practical difference is there between reducing the VBW and just plain averaging? I know that reducing the VBW is actually filtering the higher frequencies, as opposed to just plain averaging. Leaving the math aside, I notice that both approaches increase the sweep time and don't have an effect on the noise floor.
Can you comment on the differences of both? When would I use one or the other?
Thanks!
Daniel Rojas You can think of the VBW as a trace smoothing filter. Thus, if you had a low level signal buried in the grass, the smoothing would likely hide the signal - while averaging would smooth out the grass but not clip the tiny signal.
This is excellent. "Yes, slower sweep speeds in a swept analyzer make it easier to find transients." I have to take periodic measurements of pulsed microwave (RADAR transmitters to be exact) signals. With one of our handheld analyzers (Agilent N9344C), I have to play with the sweep speed, or the signal will pop in and out of view, or it won't display at all. The analyzer is basically DC to 20GHz and has no problem reading CW signals at any of the frequencies we check (anywhere from 700MHz to about 9 GHz). We sometimes borrow a Rohde and Schwarz FSH20 handheld that displays any signal we want to see without touching any settings. I'm wondering if there was something I missed in the spec sheet when I acquired the Agilent, or is the Rohde and Schwarz just more refined?
Another great example of American way of teaching by super talented yet humble masters. Thank you!
What is "American way of teaching"?
@@jimcervantes5659 glad u asked. American way Of teaching is: 1) spoken by someone with both theory and practical knowledge 2) taught using actual hardware and NOT text book or black board 3) spoken from years of personal experience and not just parroting 4) taught humbly, simply, and to the point using fewest words
Baki Pest - Why do you refer to it as American?
@@jimcervantes5659 because America is number 1 in high-tech. From moon landing to smart phones, and just about anything me/you use is invented in America, definitely much more advanced than mine (india) or your (Mexico, spain?) country
Baki Pest - I am a US citizen and have received all of my education in the US, including a BS in electrical engineering. Nothing in your description seems inherently American, nor necessarily optimal depending on the circumstance. I have seen a lot of American teaching and don't recognize what you are talking about. Oh well.
Im familiar with RF and spec ans and I’ll tell you what - it’s a very good video for a novice to watch. I think repetition and doing so every so often (it’s easy to forget setups/applications).
In my line of work, I try to familiarize myself with Markers, Min and Max holds. Measuring channel and composite power. Eb/no, signal to noise, etc. Runnings sweeps on cables. Spec ans are also used in conjunction with signal generators (sig-gen) when testing RF equipment, fiber shelves or RF antenna paths. Blah blah.
These are excellent fundamental refresher videos. Very well thought out and explained. Backed by excellent examples on real world equipment. Very nice.
This is just the video that I was looking for a long time ago . Wonderful
Best RUclips video I've seen on how a spectrum analyser works. Clear simple description. Great stuff keep it coming!
I had never seen a description of RBW using a mask (to represent the RBW filter) over a drawing of the measured spectrum. It was very easy to understand.
your visual examples coupled with your explanation as you go makes this a great tutorial, thanks!!
Very useful and concise information, and very applicable to modern SA's such as Rigol and Siglent. Thanks! Peter G6EPN
EXCELLENT explanation Alan!!! Much appreciated on this end. I have just bought a spectrum analyzer off eBay and I think I will love it!! Keep it up!!!
Hello Alan. Another very useful, clear video. Found it very helpful in the use of my new spectrum analyzer; allowing me to use the equipment more effectively and more 'knowingly'. Thanks
Your videos are amazing. I don't understand why teachers can't expalin it that well
Teachers can usually only teach. They usually don't understand the real meaning of what they teach. Most of them time, they simply memorize things.
Wow ! .... Very nicely explained. It cleared my doubts and will definitely help me. Thanks a lot.
thanks for the great explanation 10 years ago!
Wish I'd bumped into w2aew years ago, great teacher, great content, many, many thanks for all.
Hey there,
Insanely good.
Your video just helped me out a lot.
Good work man, and thanks.
Greetings from Germany
What a brilliant explanation!! Congratulations!.. this goes straight to my classroom and lab.
Very helpful explanation, particularly with the paper prototype (Wide Band and Narrow Band). Thank you.
Such a brilliant demonstration video! Very informative! Thanks w2aew, you're the best!
Thank you for such clear & concise explanation! You've saved me so much time and effort at work.
Super well explained with just a pen and cutout cardboard. Like it a lot! thanks!
THANK YOU!!! Now I understand the different.
Best video ever! You are a hero !
It was the last question in my last oral exam of my master degree. Thanks for sharing your knowledge.
Thanks from Brazil, i'm working with BK Precision by micronix, and that video helps me a lot!!!!
I´ll see the others videos to learn more about it!!! Thank you!
The block diagram, teaching materials and your way of explanation are very succinct. You are very knowledgeable. I am hoping for Oscilloscope operating tutorial video clips when you have a chance. Thank you very much.
I have MANY videos on operating oscilloscopes. Here's a playlist:
ruclips.net/p/PL746BF38BC2E068E0
@@w2aew Thank you very much for the information. Please excuse me for not searching about Oscilloscope tutorials thoroughly before requesting. No matter how complex a piece of equipment, you make it so simple to understand
Very nice presentation & explanation of the resolution bandwidth
Amazing explanation. I have never seen such a great tutorial of a SpecAn. Thanks !!
Excellent video to detail how RBW works.
Thank you so much. It's helping me a lot in my EE courses. Your videos are so unique and informative!
Very glad to hear that my videos are helping in your coursework!
This is an awesome explanation
Love how clear this was
Thank you! Very clear both in theory and practical. Solved my confusion for a long time.
The best explanation I've ever heard before. Thanks.
Thank you for the explanation. I’m still learning a few tips and tricks from you combined with my operator’s manual on my newly acquired SA (HP8560E). I have learned a lot from you =)
Excellent explanation; concise and clear: direct to the point. Thank you!
just 1 word: beautiful !!!!
Great demonstration really helped me understand what is happening! Thank you!
This is a pretty decent knowledge bank video. Thanks for uploading and so lucidly explaining the concepts.
Great presentation and illustrations. Thank you very much.
Alan, fascinating. A few questions from this presentation:
1. What is model of analyzer for demo?
2. If video bandwidth is reduced the amplitude of noise is also reduced and as it is a low pass filter is there a slight reduction in overall amplitude (and therefore accuracy)?
3. You mentioned reducing video bandwidth might uncover stuff that would be masked in the noise. You mean a transient that does not go above the noise floor (of previous wider bandwidth)?
4. Would reducing the sweep span (I should watch prior video as term is not known) reduce horizontal sweep time and therefore increase resolution of transients?
Many thanks for considering my questions!
/k1mgy
I've never seen this explained so well.
So is the video bandwidth similar to the averaging on a digital scope? Very informative video, thankyou.
Great tutorial. Thanks for producing this videos. Please keep on with it.
Amazing video!!! Simple, concise and super clear!!!!! Thanks a lot.
Very innovative way of explaining ! Great work !
Thank you veeeeery much for this very useful video!!!!!
Thank you from Russia! More happiness to your life!
Thanks Alan
Another great informative video. Nice explanation of interaction of RBW and VBW..
I get so much from your sessions!
Thank you!
Thanks for the clear and concise explanation!
Love you videos. Along the lines of filters, Tek made a notch filter plugin for calibrating their low noise oscillator years ago. The notch filter attenuated the target Freq by about -60db with a very sharp Q factor. I’d like to make one of these but don’t really I stand how to get such a narrow but deep attenuation. I bet you could make this into a great video. The Tek device was the Tektronix 067-0938-00 Notch Filter Calibration Fixture for calibrating the Tek SG505 low freq oscillator.
High Q narrowband notch filters are tricky to make. Resonant cavities are one way - check out my video on tuning a notch type duplexer.
yes, you deserve 10 times more views …. my respect !
I have enjoyed all the videos that i have seen and learned very much. Can you make a video on how to determine what the noise floor power is? Since the RBW can lower the DANL, how can I determine which RBW to use when finding the noise floor power level? I know the lowest noise floor for a 10 MHz channel is -104 dBm. Which my spectrum analyzer at 100kHz RBW with pre-amp on, I can view a noise floor of -114 dBm. This must be because of the Noise figure of the SpecA. -174+10log(100,000)+10=-114 dBm. This would allow me to view the noise floor of -104dBm but how can I determine which RBW to use if I'm viewing a 10 MHz LTE uplink signal being transmitted from a BDA? Would I just use -104dBm + noise figure and gain of BDA and set the RBW below that noise level? I believe I might need to use a noise marker since that dBm value would be much higher than the DANL of 100kHz RBW. Anyways, I look forward to learning from you and if you could give me any guidance and correction, I would greatly appreciate it. Thank you.
Someone below asked why spectrum analysers are so expensive, my one uses basically an oscilloscope mainframe but with a spectrum analyser "plugin". One of the expensive to replace parts of a spectrum analyser is the mixer, they are easily destroyed but probably the most vulnerable component. The mixers have to have a broad, flat frequency response and tend to use exotic diodes within them. Sadly I have seen spectrum analysers effectively written off due to mixer damage.
I am sure the precision attenuators are not cheap either!
Very very smart explanation :).
Btw did u have any issues with these advantest sa's? Mine was similar model but some day noise appeared around all carriers even the LO leakage was noisy and the level droped all down... I suspect mixer said enough for this life, i wish yours last long because advantest people does not share any service manual
Wonderful explanation and demonstration of R&V BW...3 Cheers!
Very concise and nicely conveyed. Well done.
Thank you for the clear explanation, would you please also explain how these can implemented with real components? I am imagining for RBW we need a variable Q band pass filter, or switching between many band pass filters. I was wondering if you can refer to some actual components or evaluation board for implementing this. Many thanks,
Excellent video! Both precise and coherent
Hi Alan, thanks for the excellent video. I am trying to understand exactly what VBW does. I do not have such a nice picture of convolving it with a signal. Could you explain more what it's cutoff frequency refers to? If I understand correctly, it cuts off all the variation faster than the set frequency after the power detector. But the speed of such variations depends on the sweep time, right? If I set a very small RBW and a large span, my VBW can still be larger than RBW without affecting the reading? Thanks :) hope you still answer to comment under your old videos.
If the VBW is set to something larger than the RBW, then is has no effect. The VBW is a low-pass filter applied to the output of the RF detector, smoothing the variations of the power detected. The lower the VBW, the smoother the trace will be because the variations will be smoothed further. Think of it as a shock absorber on the output of the detector. The stronger the damping rate (lower BW), the less variation you'll see in the trace.
@@w2aew Thanks for the answer! Yeah, that's what I thought. I'm trying to understand it's relationship to RBW, might need some time to figure out the mathematical intuition there. I'm using spectrum analyzer to hopefully extract a phase noise from an instrument, so I would like as little unknown filtering as possible. Just convolving with RBW filter seems reasonable. Thanks again for the videos, they helped me understand the spectrum analyzer pretty well, and for your answer :)
Hi w2aew .. Excellent explanation .. Nobody ever explained it this way to me.
Thank you so much for this ilustrative explanation, it helped me a lot!
It is an excellent explanation. Would you please explain about the effect of the ratio VBW to RBW on uncertainty of power measurement (eg channel power)? for example why it is necessary to set VBW >=3*RBW for having negligible bias that arises due to log power averaging . Thanks a lot.
I just shared this with my students. Great job.
That's great! Feel free to share any of my videos with them that you might find useful. I have lots of circuit tutorials, component tutorials, test & measurement topics, and much more on my channel.
This is a superb explanation of RBW and VBW. Chapeau!
I have one question though: am I right in understanding that a smaller RBW lowers the noise floor simply because the detector is integrating the power over a smaller frequency range, or is there some other effect in play?
Exactly right - a smaller RBW "sees" a narrower bandwidth, so it sees less total noise.
Excellent !, thank you for the detailed explanation and live demonstration
it looks like the narrow rbw filter would generate some plateaus, since the given tones stay in it for a while when it sweeps them, so the graph at the bottom would not be sharp at the top, but rather flat, but still narrower than the graph above it.
Well, not really. In reality, the filters typically have a Gaussian shape, and resulting spectrum trace of a single frequency tone will show the shape of the filter.
Great videos. Thanks for taking the time to make these :)
Can I ask you a few questions? In measuring the output power of a radio transmitter, which will give me a more accurate measurement? A power meter or a Spectrum Analyzer? Also, is the power I'm measuring peak or average? I was told using a zero span will give a better peak power measurement instead of a bigger span. Why is that?
In general, a proper RF power meter will give you a more accurate power result than a spectrum analyzer. They are available for both average and peak power measurement. Zero span on a spectrum analyzer will give you a decent result as long as the RBW is wider than the bandwidth of the signal you're measuring.
Fascinating, Knowledgeable and clears all doubts Thanks
Sensational videos. 73!
Excellent explanation, well presented
Amazing video!!! Thank you
Absolutely superb explanation. Thank you!!
Wow! What an explanation! Thank you sir!
Awesome explanation!
Hi there Any chance for a help here I want to measure EMF There is a device that produces an EM radiation and I wanted to find out all the details about it Any chance what tools I would need Thx
Also For radio frequency measuring Thx for getting back to me
Excelente video! Muy completo, y gracias a esto me permitio reforzar conocimientos. Gracias